Electroluminescent (EL) devices based on organic thin layers have recently attracted much attention because of their potential uses in large-area flat-panel displays and light-emitting diodes (LED). Organic LEDs have been made with both low molecular-weight organic materials and with polymers. The performance of these devices is significantly influenced by the charge balance between electrons and holes from opposite electrodes. The charge can be balanced by using a bilayer structure including a hole transporting layer and an electron transporting layer. One or both of these layers can be luminescent.
An important quality of organic EL materials is their durability, i.e., thermal and morphological stability. Thus, it is desirable that organic EL materials are not only light-emitting and hole-transporting, but also robust.
This invention relates to substituted carbazole compounds, which are hole-transporting, light-emitting molecules with high glass transition temperatures. These compounds have a number of qualities that make them useful in electroluminescence devices.
In one aspect, the present invention features substituted carbazole compounds of formula (I): 
Each of Z1 and Z2, independently, is 
[referred to hereinafter as N(R2R3), A1Y1, or A2Y2N(R4R5)]; each of A1 and A2, independently, is S, O, NR, or CHxe2x95x90CH; each of Y1 and Y2, independently, is aryl or heteroaryl; each of R1-R5, independently, is aryl or heteroaryl; and each of R6-R11, independently, is H, CN, alkyl, OR, NRRxe2x80x2, COR, or C(O)OR; in which each of R and Rxe2x80x2, independently, is H or alkyl. Note that Z1 and Z2 can be two different N(R2R3), two different A1Y1, or two different A2Y2N(R4R4R5).
Referring to formula (I), a subset of the carbazole compounds of this invention is featured by that each of Z1 and Z2, independently, is N(R2R3). In these compounds, each of R6-R11 can be H; R1 can be phenyl; each of R2 and R3, independently, can be aryl. In some embodiments, one of R2 and R3 is pyrenyl and the other is phenyl. Exemplary compounds include 9-N,Nxe2x80x2-triphenyl-N,Nxe2x80x2-di-pyren-1-yl-9H-carbazole-3,6-diamine (Compound 1), 9-phenyl-N,Nxe2x80x2-di-pyren-1-yl-N,Nxe2x80x2-di-p-tolyl-9H-carbazole-3,6-diamine (Compound 2), and N,Nxe2x80x2-bis-(4-methoxy-phenyl)-9-phenyl-N,Nxe2x80x2-di-pyren-1-yl-9H-carbazole-3,6-diamine (Compound 3).
Another subset of the carbazole compounds of this invention is featured by that each of Z1 and Z2, independently, is A2Y2N(R4R5). In these compounds, A2 can be S; each of R6-R11 can be H; R1 can be phenyl; each of R4 and R5, independently, can be phenyl. In some embodiments, Y2 is phenyl, carbazolyl, or fluorenyl. Exemplary compounds include 9-phenyl-3,6-bis{5-[4-diphenylamino-phenyl]-thiophen-2-yl}-9H-carbazole (Compound 4), 9-phenyl-3,6-bis{5-[3,5-bis(diphenylamino)-phenyl]-thiophen-2-yl}-9H-carbazole (Compound 5), 9-phenyl-3,6-bis[5-(3-diphenylamino-9-ethyl-carbazol-6-yl)-thiophen-2-yl]-9H-carbazole (Compound 6), or 9-phenyl-3,6-bis[5-(2-di-phenylamino-9,9-diethyl-fluoren-7-yl)-thiophen-2-yl]-9H-carbazole (Compound 7).
Further, another subset of the carbazole compounds of this invention is featured by that each of Z1 and Z2, independently, is A1Y1. In these compounds, A1 can be S; and Y1 can be heteroaryl. An exemplary compound is 9-phenyl-3,6-bis[5-(carbazol-3-yl)-thiophen-2-yl]-9H-carbazole (Compound 8).
Still further another subset of the carbazole compounds of this invention is featured by that one of Z1 and Z2 is N(R2R3) and the other is A1Y1.
In addition, salts of the carbazole compounds described above are within the scope of the invention. For example, a salt can be formed between a positively charged amino substituent and a negatively charged counterion.
Alkyl, aryl, heteroaryl, phenyl, pyrenyl, carbazolyl, and fluorenyl mentioned above include both substituted and unsubstituted moieties. The term xe2x80x9csubstitutedxe2x80x9d refers to one or more substituents (which may be the same or different), each replacing a hydrogen atom. Examples of substituents include, but are not limited to, halogen, amino, alkylamino, arylamino, dialkylamino, diarylamino, hydroxyl, mercapto, cyano, nitro, C1xcx9cC6 alkyl, C1xcx9cC6 alkenyl, C1xcx9cC6 alkoxy, aryl, heteroaryl, or heterocyclyl, wherein alkyl, alkenyl, alkoxy, aryl, heteroaryl, and heterocyclyl are optionally substituted with C1xcx9cC6 alkyl, halogen, amino, alkylamino, arylamino, dialkylamino, diarylamino, hydroxyl, mercapto, cyano, or nitro. The term xe2x80x9carylxe2x80x9d refers to a hydrocarbon ring system having at least one aromatic ring. Examples of aryl moieties include, but are not limited to, phenyl, naphthyl, and pyrenyl. The term xe2x80x9cheteroarylxe2x80x9d refers to a hydrocarbon ring system having at least one aromatic ring which contains at least one heteroatom such as O, N, or S. Examples of heteroaryl moieties include, but are not limited to, pyridinyl, carbazolyl, and indolyl.
In another aspect, this invention features an electroluminescence device made with one or more of the carbazole compounds described above. The device includes a hole transporting layer, an emitting layer, and an electron transporting layer. The hole transporting layer, the emitting layer and the electron transporting layer are disposed in the above order, and at least one of the hole transporting layer and the emitting layer includes the carbazole compounds of this invention. In some embodiments, both the hole transporting layer and the emitting layer include the carbazole compounds.
The details of one or more embodiments of the invention are set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
The invention features carbazole compounds, and EL devices made using these compounds. In particular, the carbazole compounds are substituted at the 3-, 6-, and 9-positions. The substituted carbazoles improve the thermal stability and/or glassy state durability of organic compounds when incorporated into the cores of these compounds and are thus useful for making organic LEDs.
A method for synthesizing certain substituted carbazoles follows: A 9-substituted carbazole is prepared by coupling a carbazole with a halide in the presence of a catalyst. Examples of suitable halides include aryl halides and heteroaryl halides, in which the aryl groups may be substituted. Other examples of suitable halides include alkyl halides and vinyl halides. The result of the coupling reaction is a 9-substituted carbazole.
The 1, 2, 4, 5, 7, and 8-positions of the starting carbazole may be H, or they may be CN, allyl, OR, NRRxe2x80x2, COR, or C(O)OR; wherein each of R and Rxe2x80x2, independently, is H or alkyl. Thus, other positions of the carbazole may be substituted; however, the product of the coupling reaction will be referred to simply as a xe2x80x9c9-substituted carbazolexe2x80x9d for brevity.
The 9-substituted carbazole is converted to a 9-substituted, 3,6-dihalocarbazole by treating the 9-substituted carbazole with a halogenating agent. The 9-substituted, 3,6-dihalocarbazole is converted to a 9-substituted, 3,6-diaminocarbazole by coupling the dihalo compound with an amine, or a mixture of amines in presence of a catalyst, such as a catalyst developed by Koie (Nishiyama et al. (1998) Tetrahedron Lett. 39: 617), or Hartwig (Hartwig et al. (1999) J. Org. Chem. 64: 5575). The catalyst shown in Scheme 1, Pd(dba)2 (dba=dibenzylideneacetone)/P(t-Bu)3, in the presence of NaO-t-Bu, can efficiently catalyze Cxe2x80x94N bond formation between an aryl halide and an aryl amine
Secondary amines are preferred in the just-described reaction; the amines can be symmetrical or asymmetric. The amines can have saturated or unsaturated aliphatic substituents, or aromatic substituents, with aromatic substituents, especially fused aromatic substituents, being preferred. The aliphatic or aromatic substituents can in turn be substituted with various functional groups, including both electron-donating groups and electron-withdrawing groups. The secondary amines can be prepared by coupling primary amines with halides in the presence of a catalyst.
Shown below is a scheme (Scheme 1) that depicts synthesis of Compounds 1-3.
A method for synthesizing other substituted carbazoles follows: A 9-substituted, 3,6-dihalocarbazole is obtained by the method described above. The 9-substituted, 3,6-dihalocarbazole can be converted to a 9-substituted, 3,6-thiophene-substituted triarylamines by coupling the dihalo compound with a thiophene-substituted triarylamine intermediate. The intermediate can be prepared through two different routes (Scheme 2). In route A, an aromatic dihalide is monothienylated by a Stille coupling reaction with thienyl tri-n-butyl stannane, followed by a Cxe2x80x94N coupling reaction with diarylamine to produce the desired intermediate. Alternatively (route B), a triarylamine is first monobrominated by, e.g., NBS/DMF, followed by palldium(0) catalyzed corss-coupling of the bromo derivative with thienyl tri-n-butyl stannane to form a thienyl-triarylamine congener. The thiophene derivative is conveniently converted into the required stannanes by a procedure involving lithiation followed by quenching with tri-n-butyl tin chloride. See, for example, Wu et al. (2000) Adv. Mater. 12: 668 and Wu et al. (1999) J. Am. Chem. Soc. 121: 472.
The thiophene shown in Scheme 2 can be replaced by furan, pyrrole, or benzene. The 3- or 6-position of carbazole can also be substituted with an oligo-aryl chain, such as the carbazol-thiophen present in Compound 8.
The compounds of the invention can be used to make EL devices. A diagrammatic representation of such a device is shown below: 
Electroluminescence devices generally include multiple layers. A typical device includes a substrate (e.g., glass), which may be coated with an oxide. The device also includes a hole transporting layer, an electron transporting layer, and an emitting layer. The hole transporting layer and the emitting layer may be combined into a single layer, or the emitting layer and the electron transporting layer may be combined into a single layer. The devices may also include a cathode.
The compounds of the invention can be used in the hole-transporting layer, the emitting layer, or in both layers.
Without further elaboration, it is believed that one skilled in the art can, based on the description herein, utilize the present invention to its fullest extent. All publications recited herein are hereby incorporated by reference in their entirety. The following specific examples, which describe the synthesis of various compounds of the invention, are therefore to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way.